Toner which develops electrical or electrostatic images is employed in various image forming techniques or recording techniques.
The toner has been produced by a grinding method wherein a thermoplastic resin is fused and uniformly mixed with a colorant (e.g. dye or pigment) and ground, followed by classifying to a desired particle size. The grinding method can produce good toner in some extent, but has a limitation in selectivity of resin. In other words, the resin which is used for the toner is required to be brittle for grinding, but the brittle resin forms a large amount of resin particles which are too small. The brittle resin also forms such too small particles in a copy machine.
In order to overcome the problems of the grinding method, Japanese Kokai Publication (unexamined) 10231/1961 proposes a suspension polymerization method wherein polymerizable monomers, colorant, initiator and charge controller are mixed in water to form a suspension and then polymerized to obtain resin particles having a desired particle size. The toner obtained by this method, however, has very broad particle size distribution for which a classification step is essential, thus resulting in poor yield. This problem is worse for such small toner that its particle size has recently been required 3 to 7 micrometer.
Japanese Kokai Publications (unexamined)273552/1986 and 73276/1987 propose a nonaqueous dispersion polymerization wherein monomers are polymerized in the presence of a pigment in a solvent which dissolves the monomers and which does not dissolve the polymerized particles. However, in this method, it is very difficult to disperse a pigment in the obtained resin particles. There may occur a flocculation of the pigment in the polymerizing system or may be free pigment flocculations present outside the polymerized resin particles.